according to Herschel's twitter (ESAHerschel) they will observe comet Honda-Mrkos-Pajdusakova on Aug 15/16. This small, short period comet has always fascinated me since it was to be flown by "tail first" by Sakigake. Too bad contact with the probe was lost before

Paolo

Aug 21 2011, 04:28 PM

from Herschel's twitter:

QUOTE

Quick look analysis of the Comet 45P/Honda-Mrkos-Pajdusakova observations by Herschel is revealing some wonderful data.

according to tweets by Daniel Fischer (@cosmos4u), Herschel should run out of coolant in March 2013 and ESA is considering end of mission scenarios. Warm observations are not possible, so one idea is to deorbit it from L2 and crash it on the Moon to perform scientific observations.

funny enough: it was also one of the possible end of mission scenarios for Chang'e 2. flying it back from L2 to impact the Moon for science

tanjent

Oct 27 2012, 01:13 PM

Is the hardware actually damaged by the lack of coolant? If Herschel were placed somewhere where it could conceivably be restocked with consumables at some future time, could it be returned to service? I guess the people who don't want to crash it probably envision some Hubble-inspired scenario like that. I recall though, that the last Hubble service call had to be performed before the gyros and other components ceased to function entirely. It wasn't something that could wait 100 years.

Paolo

Oct 27 2012, 01:57 PM

I see at least three reasons why this is not doable:1. unlike the HST, Herschel was not designed to be serviceable2. you need to use fuel to keep it into the halo orbit or to redirect it somewhere else to wait for servicing. I understand that fuel remaining is not a issue now, but it will become at a certain moment3. orbital refuelling has been carried out until now with storable, room temperature liquids (hydrazine and water mostly). transfer of cryogenic fuels has yet to be tested, not to speak of the transfer of super-cold (less than 5K IIRC) liquid helium

Phil Stooke

Oct 27 2012, 08:14 PM

Paolo said "funny enough: it was also one of the possible end of mission scenarios for Chang'e 2. flying it back from L2 to impact the Moon for science"

Strictly speaking the Toutatis flyby is not an end of mission scenario. The question is, what is the post-Toutatis trajectory? I am assuming for lack of other information that the spacecraft will not get very far from Earth and its orbit will bring it back, rather than heading off into a more distant heliocentric orbit. Is there any description of its current orbit?

Phil

Paolo

Oct 29 2012, 02:57 PM

some insight on the decision to crash Herschel and the possible alternatives on this bloghttp://herschellife.blogspot.es/1342197754...-end-of-helium/I would have loved the Herschel trailblazer concept: placing Herschel at the Earth-Moon L2 point to perform tests for future farside communication satellites before crashing it to the surface. unfortunately, the option was apparently deemed too expensive

Probably a stupid question, but I'm guessing that the wavelengths being observed are too far into the infrared to allow a warm mission, ala Spitzer?Seems like a lack of foresight (or penny pinching) to put up such a huge mirror, and not leave any instruments that could take advantage of it in an extended mission.

For a telescope operating at shorter wavelengths (about ten times longer in wavelength than visible light) a “warm mission” is feasible. This could have been done with Herschel, but it would have required that the surface of the telescope be made far more precise and smooth. That would have made it very much more expensive, leaving less money available for the rest of the spacecraft and the instruments.

Any space mission must be built within a certain budget, and it is usually best to design it to be as effective as possible for a certain wavelength range. Herschel actually covers a very wide range – from 55 to nearly 700 microns in wavelength. That’s more than a factor of ten, which is very impressive. To make a warm mission possible would have meant making the telescope good enough to work at ten times shorter wavelength, and adding a fourth instrument.

Paolo

Apr 30 2013, 04:58 PM

by the way, the radiation monitors are still useable, and there was a proposal to keep them on. hope they will do it...

The ESA Space Weather Team is keen to maintain Herschel operational as long as possible because of the information that it provides on the radiation environment in Deep Space. Herschel will finish observing just as we reach solar maximum, so any time that it can spend after solar maximum will be a tremendous bonus, particularly if it could observe for a full solar cycle. For this, it does not matter of Herschel is in the Earth-Sun L2, the Earth-Moon L2, or in heliocentric orbit: the environment is similar and totally different to that in low-Earth orbit, where most satellites are, protected by the Earth’s magnetic field.